pg_basebackup error

A user sometimes gets the following errors while running pg_basebackup:

```
pg_basebackup ERROR: invalid segment number 0 in file "224_1.data"
pg_basebackup WARNING: 5 temporary files and directories not closed at end-of-transaction
```

and

```
pg_basebackup: error: COPY stream ended before last file was finished
```

I suspect these might be happening when pg_basebackup tries to copy contents of `$PGDATA/base/pgsql_job_cache`, while a concurrent transaction tries to delete directories from there. But I haven't been able to reproduce the error myself.